Drilling fluids employing synthetic fluids (i.e., monoester-based drilling fluids) as the base fluid are capable of achieving 96 hour LC50 Mysid shrimp (Mysidopsis bahia) bioassay test results greater than 100,000 ppm. However, even with these bioassay test results their commercial use has been severely restricted.
Accordingly, there is a need for a drilling fluid which employs an inexpensive, non-toxic synthetic fluid as the base fluid. The present invention satisfies this need by providing a drilling fluid comprising: (a) at least one drilling fluid additive (e.g., an emulsifier, a viscosifier, a weighting agent, and an oil-wetting agent) and (b) an inexpensive, non-toxic base fluid composed of monoester(s).
Previously, it has been reported that secondary esters can be used with invert drilling muds, wherein the esters comprised of C1-C5 carboxylic acids and one or more C3-C22 olefins (see U.S. Pat. Nos. 6,100,223 and 6,191,076). Furthermore, the related U.S. patent application Ser. No. 13/682,542 (Monoester-Based Lubricants and Methods of Making Same), filed Nov. 20, 2012, and incorporated in its entirety herein, provides a simpler, more efficient method of preparing monoesters.
As such, it would be extremely useful and desirable to employ methods of drilling a borehole in a subterranean formation with a biodegradable and non-toxic monoester-based drilling fluid, particularly when such methods utilize renewable raw materials in combination with converting low value Fischer-Tropsch (FT) olefins and alcohols to high value monoester-based drilling fluids.
In this aspect, it has been found that the monoesters prepared from C6-C41 carboxylic acids and C8-C84 olefins of the subject invention provide excellent properties for use in drilling fluids. In particular, the monoesters of this invention have a lower viscosity and excellent gel strength at high temperature and pressure than the current commercially available esters on the market today.